Recently, with prevalence of the Internet, mobile phones, digital broadcasting etc., digital communications in which digital signals are transmitted and received are widely carried out. When digital communications are carried out via a transmission path, waveform distortions such as intersymbol interference occur due to transmission properties of the transmission path. In order to deal with this problem, equalizers for compensating waveform distortions have been used conventionally.
In general, equalizers having been used conventionally (hereinafter referred to as conventional equalizers) compensate waveform distortions based on linear operation. Specifically, as shown in FIG. 19, most equalizers include transversal linear filters for calculating a linearly weighted sum of a received signal. Linear filters shown in FIG. 19 are s-tap linear filters (s indicates a positive integer of 3 or greater). That is, each linear filter in FIG. 19 includes s−1 unit delay elements Dt (t=1, 2, . . . , and s−1), s multiplication sections Mu (u=1, 2, . . . , and s), and an addition section ADD.
Further, in a case where transmission properties change temporally, adaptive equalizers which learn a coefficient Cu (u=1, 2, . . . , and s) of a multiplication section Mu in accordance with the transmission properties are used generally.
As for a technique relating to equalizers, Patent Literature 1 discloses a technique for compensating group delay distortions by using a phase equalizer. The technique disclosed in Patent Literature 1 is a kind of a method for demodulating a modulated signal having group delay distortions, designed to learn phase variation history and phase errors based on information regarding a received signal point so as to correct phase distortion.